Method of making expanded integral fin sheet metal tubing for use in heat exchangers

ABSTRACT

A SHEET METAL TUBING HAVING INTEGRALLY FORMED WEB SECTIONS WHICH ARE SLIT TO FORM FINS. THE FIN SURFACE AREA IS INCREASED BY CORRUGATING THE WEB SECTIONS PRIOR TO SLITTING THEM INTO FINS. AFTER SLITTING, THE FINS ARE FLATTENED OR SHAPED AS DESIRED, AND THEN TWISTED OR BENT TO FORM THE DESIRED ARRAY. THE SHEET METAL TUBING MAY BE FORMED INTO A VARIETY OF SHAPES SUCH AS COILS FOR USE IN HEAT EXCHANGERS IN APPLICATIONS SUCH AS REFRIGERATORS.

Oct. 12, 1971 KElTH 3,611,534

METHOD OF MAKING EX A DED INTEG FIN SHEET METAL TUBING FOR USE IN HEAT HANGERS Filed Sept. 25, 1969 3 Sheets-Sheet 1 FIG '10 FIG -1 -]1 INVLNTOR.

' NORVAL A. KEITH Oct. 12, 1971 Err 3,611,534

METHOD OF MAKING EXPANDED INTEGRAL FIN SHEET METAL TUBING FOR USE IN HEAT EXCHANGERS Filed Sept. 25, 1969 3 Sheets-Sheet 8 INVENTOR NORVAL A. KEITH BY Zm/ ATTORNEY Oct. 12, 1971 KE|TH 3,611,534

METHOD OF MAKING EXPANDED INTEGRAL FIN SHEET METAL TUBING FOR USE IN HEAT EXCHANGERS Filed Sept. 25, 1969 3 Sheets-Sheet 3 INVENTOR I I NORVAL A. KEITH QB/MM ATTORNEY United States Patent Office Patented Oct. 12, 1971 US. Cl. 29157.3 V 5 Claims ABSTRACT OF THE DISCLOSURE A sheet metal tubing having integrally formed web sections which are slit to form fins. The fin surface area is increased by corrugating the web sections prior to slitting them into fins. After slitting, the fins are flattened or shaped as desired, and then twisted or bent to form the desired array. The sheet metal tubing may be formed into a variety of shapes such as coils for use in heat exchangers in applications such as refrigerators.

This application is a continuation-in-part of application Ser. No. 774,577, filed Nov. 1, 1968, now Pat. No. 3,495,657, which in turn is a continuation of application Ser. No. 630,376, filed Apr. 12, 1967, now abandoned. This application is also a continuation-in-part of application Ser. No. 708,463, filed Dec. 7, 1967, now abandoned. This invention relates to a hollow sheet metal article and more particularly to sheet metal tubing having integral fins extending externally therefrom for use in a heat exchanger. The invention relates to sheet metal tubing having integral fins, wherein the fins have been expanded to increase their surface area.

In parent application Ser. No. 774,577, filed Nov. 1, 1968, by N. A. Keith, assigned to the assignee of the instant invention, there is disclosed a sheet metal tubing having an integral fin structure. The fins therein disclosed are formed by slitting the web sections of the sheet metal tubing, and bending or bending and twisting the slit portions to form fins. It has been found that a heat exchanger made from sheet metal tubing having integral fins as disclosed in the companion case, is susceptible in some applications, such as in a frost free refrigerator, to frost or ice build up, which blocks the air flow between the fins of the heat exchanger. Although the fin surface area available is suflicient for purposes of heat transfer, there tends to be insufficient surface available for adequate frost and ice build up. The instant invention represents an improvement on the integral fin sheet metal tubing disclosed in the companion case in that the fins are expanded to provide a greater surface area and thereby reduce the frost and ice build up problem.

Processes are known in the art for increasing the surface area of fins. In Pat. No. 3,227,766 granted Jan. 18, 1966, to N. A. Keith, assigned to the assignee of the instant invention, there is disclosed one process wherein a punch and die is used to form integral fins in a hollow sheet metal article. The fins which are formed have an expanded surface area. In Pat. No. 3,294,162, granted Dec. 27, 1966, granted to H. I. Loehlein et al., there is disclosed a process of forming integral fin tubing wherein the surface area of the fins is expanded. In the processes disclosed in both of these patents, there results considerable tool wear because of the way the fins are formed. Further, the tools must be made to close tolerances.

The products produced by these processes also differ markedly from that produced in accordance with the process of the instant invention which will be more fully discussed below. For example, the Loehlein et a1. patent is restricted to the production of integral fin tubing having expanded fin area, wherein the fins are oppositely curved at their top and bottom ends. This causes turbulence and reduces the freedom of air flow between the fin surfaces. It has been found that integral fin sheet metal tubing has adequate heat transfer properties without the need for turbulent air flow between the fins. Therefore, the shape of the fins obtained by the Loehlein et al. process is not desirable because it cuts down the air fiow. i

According to the instant invention, it has been found that the fin surface area of the integral fin sheet metal tubing, made in accordance with the teachings of application Ser. No. 774,577 can be expanded by corrugating the web sections prior to slitting them into fins. The corrugation of the web sections causes the metal in the web sections to stretch and thereby increase the surface area of the fins cut from the web sections. Further, the shape of the fins is not restricted as in the Loehlein et al. patent, but may have any desired shape such as substantially fiat one.

It is accordingly an object of this invention to provide sheet metal tubing having integral fins wherein the fin surface area has been substantially expanded.

It is a further object of this invention to provide a heat exchanger employing integral fin sheet metal tubing having expanded fin surface area.

It is a still further object of this invention to provide a process for expanding the fin surface area of integral fin sheet metal tubing.

Other objects and advantages of this invention will become more apparent from the following description and drawings, in which:

FIG. 1 shows a sequence of perspective views of the sheet metal tubing in accordance with this invention after various stages of processing.

FIG. 2 shows the use of a press to obtain corrugation of the web sections of the sheet metal tubing of this invention.

FIG. 3 shows the use of a rotary corrugator to obtain corrugation of the web sections of the sheet metal tubing of this invention.

FIG. 4 is a perspective view of a heat exchanger according to the present invention.

FIG. 5 is a top view of the heat exchanger of FIG. 4.

FIG. 6 is a top view of a modification of the heat exchanger shown in FIG. 4.

Referring now to the drawings and especially to FIG. 1, there is illustrated the sheet metal tubing of this invention after various stages of processing. The sheet metal tubing in accordance with this invention may be fabricated by the method disclosed in Pat. No. 2,690,002, granted to Grenell on Sept. 28, 1954. Referring to FIG. 1a, a pattern of Weld inhibiting or stop-weld material 1 is applied to a clean surface of a strip of metal 2. A second strip of metal 3 having a cleaned surface is superimposed on the surface of the first strip, as shown in FIG. 1b, and the two sheets are secured together to prevent relative motion therebetween. Thereafter, the two superimposed strips 2 and 3 are pressure welded together by rolling so that the adjacent areas of the sheets which are not separated by the stop-weld material 4 become unified together. The rolling of the sheets results in reducing the thickness of the two superimposed strips and in elongating the resultant blank 5 in the direction of rolling, while the width of the resultant blank 5 remains substantially the same as the initial width of the strips. Following the rolling operation, the resulting blank is usually softened, as by annealing, to make it more pliable, and if desired it may be further rolled to the final gauge desired and again softened as by annealing. The stop-weld material results in the retention of unwelded portions 6 and 7 extending internally within 6 and along the edges 7 of the blank 5 and sandwiched between its outer surfaces. After softening the blank 5, the unjoined portion 6 may be expanded as in FIG. 1c, by injecting therein a fluid under pressure of sufficient magnitude to permanently deform the blank 5 in the area of the unwelded portion 6 to form the desired passageway 8. However, it is to be understood that other methods may be employed in the manufacturing of the sheet metal tubing in accordance with this invention.

The process for expanding the fin surface area of the sheet metal tubing in accordance with this invention, will now be illustrated with further reference to FIG. 1. FIG. la shows, as noted above, a portion of a strip of metal 2 having a pattern of stop-weld material 1 on its surface. The pattern of stop-weld material 1 is laid out in three stripes A, B, and C. The central stripe B will become an inflated passageway 8. The stripes A and C along the opposite edges will form web sections which will be made into fins. A second strip of metal 3 is pressure welded to the surface of the first strip of metal 2 having the stopweld pattern as shown in FIG. lb. At this point, the inflatable passageway 8, corresponding to unwelded portion 6, may be inflated as shown in FIG. 10, or it may be left uninflated until the expanded fins have been formed. It is preferred to leave the inflation of the passageway 8 till after the fins have been formed in order to avoid damage to the passageway 8.

The unwelded portions 7 form the web sections 9 from which the fins are cut. Referring to FIG. 1d, each of the web sections 9 may be separated into two webs corresponding to the unwelded portions 7. For the sake of simplicity, only the web section 9 on one side of the blank has been shown separated. After the Web sections 9 have been separated to form two webs 10 on each side of the passageway 8, each of the webs 10 is fed through a corrugating machine, which will be more fully described later, to form a corrugated surface, as shown in FIG. 1e. Again for the sake of simplicity, only one web 10 is shown to be corrugated, but it is obvious that in practice, there would be four webs 10 each of which would be corrugated. The corrugation of the web 10 causes the metal to stretch and thereby expand significantly. After the webs 10 have been corrugated, they are slit or as in FIG. 1}, cut at points 11, corresponding to the extreme edges of the corrugated webs, to form fins 12. Following the slitting operation, the fins 12 are flattened or pressed to form any desired shape, as shown in FIG. 1g. After the fins 12 have been shaped, they are twisted, if desired, to provide a better fluid flow path, and the passageway 8 inflated, as shown in FIG. 1h.

The fins 12 in FIG. 111 have been bent so that their major surfaces are substantially parallel to one another. Further, the fins have been oriented such that the heat exchange fluid flowing between the fins is directed, by virtue of their orientation, in a direction substantially perpendicular to the longitudinal axis of the fluid passageway 8. The fins may be oriented to provide for the flow of the heat exchange fluid in any desired direction.

It should be apparent that while the process has been proposed with respect to a blank having a single fluid passageway, it is equally applicable to a blank having a plurality of passageways. Further, the blank itself may be formed from a plurality of sheets of metal, each sheet having unwelded portions which may be bent apart to form webs which are then processed in accordance with the invention.

The corrugation of the webs or web sections should increase their surface area at least about 10% and preferably at least about Generally, their surface area 4 is increased about 20% to 50% although greater increases in surface area may be employed.

The sheet metal employed in the present invention is made of aluminum, aluminum alloys, copper, copper alloys, or steel. The passageways are inflated using a suitable in'flation medium, such as for example, air or water, at a pressure of approximately 500 to 3,000 p.s.i.

In the embodiment just discussed, the web sections 9 included a stop-weld pattern which permitted them to be separated so as to form four webs 10 instead of two. It is also possible to omit the use of the stop-weld pattern and thereby form only two web sections which can then be corrugated, slit, flattened, and twisted, in accordance with the invention, to form expanded integral fin sheet metal tubing.

Referring now to FIG. 1i, there is illustrated yet another embodiment of the sheet metal tubing of the invention. In this embodiment alternate fins 12 and 12' are bent in opposite directions, instead of being twisted. By virtue of the corrugation of the web, alternate fins are parallel and when bent as in FIG. 1i, two rows of parallel fins result. This embodiment is particularly useful when high heat transfer rates are required, because a tortuous path is presented to the fluid flowing about the finned surfaces.

In FIG. 2, there is illustrated one means for corrugating the web sections or webs of the sheet metal tubing of the invention. In this embodiment, a press 20 is used. Intermeshing dies 21 having the desired corrugation contour, are used to corrugate the webs 10. As the dies press the web 10 between them, they corrugate it, thereby stretching it and increasing the surface area of the web 10. The use of a press 20 employing dies 21, as shown in FIG. 2, is the preferred approach because it is possible to get any desired amount of stretching of the web surface area by merely increasing or decreasing the stroke of the dies 21. It is also possible to employ a die, not shown, which would have one section for corrugating the webs, a further section for slitting the corrugated webs and a still further section wherein the slit webs are flattened or otherwise shaped as desired.

In operation, a strip-like blank would be fed into the die and the webs corrugated. The blank would then be advanced so that new portions of the webs are corrugated and the corrugated portions are slit. As the blank is further advanced the slit portions are flattened or shaped. In this manner the process of the invention can be carried out in a somewhat continuous fashion.

To get the greatest amount of expansion and stretching, in accordance with this invention, it is preferred to clamp the web sections prior to their being corrugated. This is desirable in order to prevent slippage of the blank in the die as it is being corrugated. This clamping may be done by any suitable means, as for example, that shown in FIG. 2. The blank is clamped between clamps 22 and 23 prior to being corrugated.

A somewhat more continuous and rapid approach would 'be to employ a rotary corrugator, as shown in FIG. 3. The rotary corrugator comprises two intermeshing gear-like wheels 30. The teeth of the wheels 30 are shaped to give the desired corrugated shape to the webs 10. The intermeshing wheels 30 effectively clamp one end of the blank while the other is clamped by a clamp, not shown, or a drag 31. The use of a drag 31 is preferred because it provides for more continuous operation.

The sheet metal tubing in accordance with this invention, may be supplied in varying lengths for different applications. It is possible to produce long lengths of such material.

One embodiment of a heat exchanger employing the expanded integral fin sheet metal tubing of the invention is shown in FIGS. 4 and 5. The heat exchanger therein disclosed has fin sections 40, fluid passageway sections 41 and welded portions 42. In FIG. 4, it is seen that the sheet metal tubing has been bent into a spiral shaped coil. This coil will be used in forced air evaporators such as those presently used in refrigerators. If desired, as shown in FIG. 6, the coil may be wound to avoid the center opening 43, shown in FIG. 5. It will be apparent to those skilled n the art that the heat exchanger, in accordance with this invention, may be bent and wound into many other shapes to suit particular heat exchanger application as for example a figure -8.

It also will be apparent that the fluid passageways must be appropriately connected to sources of the heat exchange medium to be passed therethrough, as by couplings known to those skilled in the art. For instance, soldered or brazed couplings may be used, or in some instances, rubber hose type couplings may be used. The couplings are known in the art and do not form a part of the present invention, except in so far as said couplings are associated with the heat exchange components of the present invention.

The sheet metal tubing of the instant invention having integral fins of expanded surface area has many advantages over that known in the prior art as discussed above. By employing thin sheet metal, the tubing is readily formable into heat exchange configurations as shown in FIGS. 4 and 6. Further, since the Webs are of comparable thin material, and the surface area of the fins is expanded by stretching rather than gauling, the tool life of the equipment used to corrugate the webs will be significantly greater than that obtainable using prior art processes. Further, the corrugating equipment itself shown in FIGS. 2 and 3, does not have to be made to the close tolerances required when using some of the prior art equipment.

It is to be understood that the invention is not limited to the illustrations described and shown herein, which are deemed to be merely illustrative of the best modes 3 of carrying out the invention, and which are suitable of modification of form, size, arrangement of parts and details of operation. The invention rather is intended to encompass all such modifications which are within the spirit and scope of the invention.

What is claimed is:

1. A process of making integral fin sheet metal tubing comprising:

providing at least two strips of metal;

6 pressure welding together said at least two strips of metal so as to define at least one inflatable fluid passageway and at least one web section, said web section being separated from said inflatable fluid passageway by a welded portion; separating apart said strips of metal in said at least one web section to form at least two webs; corrugating said at least two webs to expand their surface area; and

cutting said webs into fins.

2. A process as in claim 1 wherein said at least two webs are corrugated to expand their surface area between about 20% and and further including the step of substantially flattening said fins.

3. A process as in claim 2 wherein the fins are then twisted to orient them so they are substantially parallel to one another.

4. A process as in claim 2 wherein the alternate fins are then bent in opposite directions to form at least two rows of substantially parallel fins.

5. A process as in claim 2 wherein the inflatable fluid passageway is inflated, using air or water at a pressure of 500 to 3,000 p.s.i.

References Cited UNITED STATES PATENTS 3,111,747 11/1963 Johnson 29--157.3 3,178,806 4/1965 Keith 29157.3 3,333,317 8/1967 Shockley 29157.3 3,368,614 2/1968 Anderson 183 X 3,434,533 3/1969 Pignal 165183 3,457,756 7/1969 Rohde 72186 FOREIGN PATENTS 112,666 1/1918 Great Britain 165-183 737,582 9/1955 Great Britain 165183 JOHN F. CAMPBELL, Primary Examiner D. C. REILEY, Assistant Examiner U.S. C1.X.R. 

